Thermoplastic forming metallic glass textures from glass molds

ABSTRACT

A thermoplastic forming method is provided for replicating the fine texture from a glass (e.g., silicate) mold.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application claims the benefit under 35 U.S.C. § 119(e) of U.S. Patent Application Ser. No. 62/646,702, entitled “THERMOPLASTIC FORMING METALLIC GLASS TEXTURES FROM GLASS MOLDS,” filed on Mar. 22, 2018, which is incorporated herein by reference in its entirety.

FIELD

The disclosure is directed to materials and methods for thermoplastic forming of metallic glass replicating the fine surface texture from a textured glass mold.

BACKGROUND

A silicate glass can have very fine surface texture after etching. Mimicking the surface structure of the silicate glass in a metallic alloy or metallic glass, however, is difficult to accomplish using conventional etching techniques. There remains a need to develop a method for achieving fine surface texture on metallic glasses or amorphous alloys.

BRIEF SUMMARY

In an embodiment, a thermoplastic forming method is provided for replicating fine texture from a silicate glass mold. The method may include placing a metallic glass in a glass mold having a portion of a surface with a fine surface texture. The method may also include heating the glass mold to a processing temperature above the glass transition temperature of the metallic glass. The method may further include applying a pressure to the silicate glass mold. The method may also include cooling the glass mold to form a metallic glass article replicating the fine surface texture from the portion of the glass mold.

In some variations, the fine surface texture of the metallic glass article varies up to 5 microns.

In some variations, the portion of the surface of the silicate glass mold is chemically etched to have the fine surface texture.

In some variations, the metallic glass comprises a material selected from a group consisting of Zr-based, Pt-based, Ni-Based, Fe-based, Ti-based, Pd-based, Au-based, Ag-based, Cu-based, Al-based, and Mo-based metallic glass.

In some variations, the processing temperature is lower than the crystallization temperature of a metallic glass.

In some variations, the article remains in an amorphous phase.

In some variations, the metallic glass has a TTT crystallization curve.

In some variations, a trajectory of the processing temperature versus time does not cross the TTT crystallization curve to void crystallization.

Additional embodiments and features are set forth in part in the description that follows, and will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed subject matter. A further understanding of the nature and advantages of the disclosure may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:

FIG. 1A shows a surface topology of a textured stainless steel mold in accordance with embodiments of the disclosure.

FIG. 1B shows the surface depth profile of FIG. 1A in accordance with embodiments of the disclosure.

FIG. 2A shows a surface topology of a textured silicate glass mold in accordance with embodiments of the disclosure.

FIG. 2B shows the surface depth profile of FIG. 2A in accordance with embodiments of the disclosure.

FIG. 3 illustrates a schematic of thermoplastic forming a metallic glass sheet into an article having a textured surface in accordance with embodiments of the disclosure.

FIG. 4 illustrates a schematic of a time-temperature-transformation (TTT) diagram for an exemplary bulk solidifying amorphous alloy in accordance with embodiments of the disclosure.

FIG. 5 is a flow chart illustrating thermoplastic forming a metallic glass with a fine texture replicating the surface texture of a silicate glass mold in accordance with embodiments of the disclosure.

FIG. 6 illustrates an image of a glass mold texture in accordance with an illustrative embodiment.

FIG. 7 illustrates a replicate texture of the glass mold of FIG. 6 for amorphous alloy Zr₇₀Cu₁₃Ni_(9.9)Al_(3.7)Nb_(3.4) in accordance with an illustrative embodiment.

FIG. 8 illustrates a replicate texture of the glass mold of FIG. 6 for amorphous alloy Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8) in accordance with an illustrative embodiment.

FIG. 9 illustrates a replicate texture of the glass mold of FIG. 6 for amorphous alloy Pt_(57.3)Cu_(14.7)Ni_(5.3)P_(22.7) in accordance with an illustrative embodiment.

DETAILED DESCRIPTION

The disclosure may be understood by reference to the following detailed description, taken in conjunction with the drawings as described below. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale.

The disclosure provides a method of thermoplastic forming a metallic glass replicating a surface texture from a silicate glass mold. The disclosure provides a method of using a silicate glass mold rather than a metal mold in the thermoplastic forming process. The silicate glass mold can obtain a very fine and/or uniform surface texture, for example, by chemical etching. Chemical etching of a crystalline metal alloy mold is non-uniform because of different etch rates of crystalline grains compared to the grain boundaries. Metal molds can have a surface texture after blasting that is quite different a surface texture of a silicate glass mold after chemical etching. The surface texture on the silicate glass mold is much finer than the surface texture on the metal molds, e.g. a stainless steel mold, which is achievable by the smallest blasting sizes. It has been found difficult to create the same fine surface texture as the silicate glass mold for metal alloys, either by etching or blasting.

As used herein, “replicating” the texture of the silicate glass refers to having similar periodicity and depth within tolerances. The mean periodicity of the metallic glass after thermoplastic forming using a silicate glass mold can be within 5% or 10% of the periodicity of the silicate glass. Likewise, the average depth can be within 5% or 10% of the depth of the silicate glass.

In addition, or as an alternative to mean periodicity, the surface texture can have a surface roughness within 30% of the Sa of the glass mold. In addition, or alternatively, the surface texture can have a surface roughness Sq within 30% of the Sq of the glass mold. In addition, or alternatively, the surface texture can have a surface roughness and/or surface depth as described herein.

The thermoplastic forming method forms an article replicating the fine surface texture of a silicate glass mold. The thermoformed article has the surface texture replicating the surface texture of the silicate glass mold. The method enables combination of the glass and metal on a product with the same texture as the glass.

Textured Glass Mold

Two variables, i.e. depth and periodicity of depth changes, may be used for characterizing surface texture. In certain variations, the depth is within +/−3 μm for both a textured silicate glass mold and a textured stainless steel mold. However, the periodicity of change in depth of the texture laterally across the surface increases for the textured silicate glass mold compared to the textured stainless steel. The increased periodicity of change in depth of the texture provides a more finely textured surface, which provides a very touch feel and look.

FIG. 1A shows a surface topology of a textured stainless steel mold in accordance with embodiments of the disclosure. FIG. 1B shows the surface depth profile of FIG. 1A in accordance with embodiments of the disclosure. The stainless steel mold (e.g. 316 SS mold) has a fine surface texture which is formed by blasting using the smallest blast sizes that can be achieved. As shown in FIG. 1B, the surface depth varies within from −1.0 μm to +1.3 μm. However, the surface profile for the stainless steel mold includes only a few peaks 102A, 102B, and 102C, for example, near 0.02 mm, 0.10 mm, and 0.22 mm, respectively. The periodicity of the texture of the 316 SS mold is relatively coarse compared to the silicate glass mold shown below. A white light interferometer (Sensofar) was used for analyzing the surface topology.

FIG. 2A shows a surface topology of a textured glass mold in accordance with embodiments of the disclosure. FIG. 2B shows the surface depth profile of FIG. 2A in accordance with embodiments of the disclosure. The glass mold has a fine surface texture which is formed by a chemical etching process. As shown in FIG. 2B, the surface depth varies within from −3 μm to +3 μm, which is larger than the depth variation from −1.0 μm to 1.3 μm for 316 SS. Also, the surface profile for the glass mold includes very sharp peaks. The number of peaks is significantly higher than the surface profile shown in FIG. 1B for stainless steel 316. For example, three sharp peaks 202A-C appear between 0.14 mm and 0.16 mm. The periodicity of the texture of the glass mold is finer than that of the stainless steel mold.

In some embodiments, the mold may be formed of glasses, such as widely used silicate glass that mainly includes (SiO₂). The optical transparency and the ability to withstand environmental influences can be considered as the most striking properties. Silicate glasses are resistant to most liquids and gases.

At room temperatures, the silicate glass can be dissolved by hydrofluoric (HF) acid or other HF-containing aqueous solutions. The silicate glass mold may be chemically etched by HF-based etchants to form the very fine surface texture. Producing texture on silicates or other glasses is not restricted to HF-containing aqueous solutions. Dry etching such as reactive ion etching can also be used.

It will be appreciated by those skilled in the art that the silicate mold may be formed of other glasses including alumina (Al₂O₃), B₂O₃, Na₂O, ZnO, LiO₂, Y₂O₃, among others.

Thermoplastic Forming of Metallic Glass

Thermoforming is a manufacturing process in which a material is heated to a forming temperature, formed into a specific shape in a mold. The sheet is heated in an oven to a high-enough temperature such that the sheet can be stretched to conform into a mold and is then cooled to a finished shape.

In various aspects, the temperature is held below the T_(g) of the silicate glass. As such, the silicate glass mold does not deform and its texture is maintained, while the texture of the metallic glass replicates the texture of the silicate glass mold. Further, the temperature profile of thermoplastic forming is maintained such that the glass mold is not thermally shocked or fractured during thermoplastic forming. Alternatively, the silicate glass mold can be fractured after thermoplastic forming and cooling, for example as a way of removing the mold.

Thermoplastic forming (TPF) of metallic glasses (e.g., bulk metallic glasses or BMGs) can be used as a fabrication method for engineered. Forming of the metallic glass takes place in the supercooled liquid region, where the metallic glass exists as a highly viscous metastable liquid. In this supercooled liquid region, the metallic glass can be formed very similar to plastics under comparable forming pressure and temperatures. The thermoplastic forming technology allows precise replication of small features with a homogeneous material, free of stresses and porosity.

The absence of a crystalline micro-structure endows the metallic glasses with a portfolio of properties such as high strength, high elasticity, and excellent corrosion resistance. Whereas the limited plasticity and hence poor workability at ambient temperature impede the structural application of metallic glasses, the superplasticity within the supercooled liquid region opens an alternative window for thermoplastic forming, which allows precise and versatile net-shaping of complex geometries on length scales ranging from nanometers to centimeters that were previously unachievable with conventional crystalline metal processing.

Unlike during die casting where cooling and forming must be carried out simultaneously, cooling is decoupled from forming during thermoplastic forming. Metallic glasses can be thermoplastically formed in their supercooled liquid region, where the required fast cooling to vitrify the metallic glass is decoupled from the mold filling operation. This is made possible by the unique crystallization behavior of metallic glasses which results in a supercooled liquid region. When an amorphous BMG sample is heated into the supercooled liquid region, the BMG first relaxes into a readily deformable supercooled liquid before the BMG crystallizes. Therefore, metallic glasses can be considered high strength metals that can be processed like plastics. Thermoplastic forming allows for more versatile and complex shapes and fine surface texture. Thermoplastic forming not only breaks through the bottleneck of the manufacture of bulk metallic glasses at ambient temperature but also offers an alluring prospect in micro-engineering applications.

The main challenge associated with processing of metallic glasses is a consequence of their metastable nature. Fast cooling conditions may be needed to avoid crystallization during processing. This limits the range of geometries that can be cast since filling of the mold and fast cooling (which require opposite ideal conditions) must be carried out simultaneously.

The thermoplastic forming method can be used for prototype or large production machines are utilized to heat and form the metallic glass and trim the formed parts from the sheet in a continuous high-speed process, and can produce many thousands of finished parts per hour depending on the machine and mold size and the size of the parts being formed.

In the thermoplastic forming process, the glass mold and the metallic glass, such as sheets, films, or rods, are heated to a temperature above the glass transition temperature T_(g) of the metallic glass.

The metallic glass or the metallic glass feedstock is formed of a glass-forming alloy and is in an amorphous phase. After thermoplastic forming at a temperature above T_(g), but below the crystallization temperature of the metallic glass T_(x), the metallic glass does not crystalize, but remains in an amorphous phase.

FIG. 3 illustrates a schematic of thermoplastic forming a metallic glass sheet into an article having a textured surface in accordance with embodiments of the disclosure.

As shown in FIG. 3, a glass mold includes an upper-half mold 310A and a lower-half mold 310B. A metallic glass sheet 312 is placed between the upper-half mold 310A and lower half-mold 310B to form an article 302, which conforms to the shape of the glass mold. The glass mold has a desired surface texture 304 on its inner surface 308. The article 302 after thermoplastic forming has a surface texture 306 which replicates the surface texture of the glass mold. The surface texture 306 is illustrated in the corresponding exploded view.

The mold is heated to above the glass transition temperature and pressure applied (arrow 305) to imprint the textured pattern of the glass mold on the softened metallic glass. In some embodiments, the glass mold is heated along with the metallic glass sheet 312 to a temperature above the glass transition temperature, and then placed in the glass mold.

The glass mold may have portions that include the textured pattern 304 and portions that remain smooth.

In some embodiments, the upper-half mold 310A has an inner surface that has a portion or the entire inner surface with a texture 304. In some embodiments, the lower-half mold 310B may have an inner surface 309 which may be textured. In some embodiments, the lower-half mold 310B not be textured.

As illustrated in FIG. 3, zones or portions of the metallic glass surface have the imprinted texture 306, and the metallic glass and the glass mold are cooled to form the desired article 302 having the desired glass article contoured shape. The resultant glass article 302 can have localized or global texture added to the glass surface useful for an improved tactile feel, or enhanced capability for the function of the glass surface, bonding other materials due to its enhanced surface area.

Texture can allow for a metallic glass surface having a controlled texture gradient, useful in functional attributes like Haze Control for various sensors or displays. Texture can be added in zones or portions of the glass and can be accomplished by gradients or steps.

The addition of texture to an article during the thermoplastic forming process is a significant advantage chemical etching of texture into an already formed article, both in complexity and precision. The textured surface added by the thermoplastic forming process is substantially free of damage caused by chemical etching, for example, scratching or etching damage. Any useful texture can be added to an article herein as long as the negative imprint can be accommodated on the mold surfaces.

In typical embodiments, the textured surface of the metallic glass article can exhibit an average surface roughness of from 0.1 to 10 μm and more typically 0.2 μm to 7 μm.

In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.1 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.2 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.3 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.4 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.5 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.6 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.7 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.8 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 0.9 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 1.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 2.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 3.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 4.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 5.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 6.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 7.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 8.0 μm. In some embodiments, the metallic glass has a surface roughness equal to or greater than 9.0 μm.

In some embodiments, the metallic glass has a surface roughness less than 0.2 μm. In some embodiments, the metallic glass has a surface roughness less than 0.3 μm. In some embodiments, the metallic glass has a surface roughness less than 0.4 μm. In some embodiments, the metallic glass has a surface roughness less than 0.5 μm. In some embodiments, the metallic glass has a surface roughness less than 0.6 μm. In some embodiments, the metallic glass has a surface roughness less than 0.7 μm. In some embodiments, the metallic glass has a surface roughness less than 0.8 μm. In some embodiments, the metallic glass has a surface roughness less than 0.9 μm. In some embodiments, the metallic glass has a surface roughness less than 1.0 μm. In some embodiments, the metallic glass has a surface roughness less than 2.0 μm. In some embodiments, the metallic glass has a surface roughness less than 3.0 μm. In some embodiments, the metallic glass has a surface roughness less than 4.0 μm. In some embodiments, the metallic glass has a surface roughness less than 5.0 μm. In some embodiments, the metallic glass has a surface roughness less than 6.0 μm. In some embodiments, the metallic glass has a surface roughness less than 7.0 μm. In some embodiments, the metallic glass has a surface roughness less than 8.0 μm. In some embodiments, the metallic glass has a surface roughness less than 9.0 μm. In some embodiments, the metallic glass has a surface roughness less than 10 μm.

It will be appreciated by those skilled in that various different textured patterns may form portions adjacent one another.

It will also be appreciated by those skilled in the art that the glass mold may vary in shapes, geometry, and/or dimensions.

The thermoplastic forming of metallic glasses always involves heat treatment. As a metastable material, metallic glasses tend to transform from amorphous to crystalline state under certain temperature. The evolution of this trend can be summarized in a temperature-time-transformation (TTT) diagram.

FIG. 4 shows the time-temperature-transformation (TTT) cooling curve of an exemplary bulk solidifying amorphous alloy, or TTT diagram. Bulk-solidifying amorphous metals do not experience a liquid/solid crystallization transformation upon cooling, as with conventional metals. Instead, the highly fluid, non-crystalline form of the metal at high temperatures (near a “melting temperature” T_(m)) becomes more viscous as the temperature is reduced (near to the glass transition temperature T_(g)), eventually taking on the outward physical properties of a conventional solid.

Even though there is no liquid/crystallization transformation for a bulk solidifying amorphous metal, a melting temperature T_(m) may be defined as the thermodynamic liquidus temperature of the corresponding crystalline phase. Under this regime, the viscosity of bulk-solidifying amorphous alloys at the melting temperature could lie in the range of about 0.1 poise to about 10,000 poise, and even sometimes under 0.01 poise. A lower viscosity at the “melting temperature” would provide faster and complete filling of intricate portions of the shell/mold with a bulk solidifying amorphous metal for forming metallic glass parts. Furthermore, the cooling rate of the molten metal to form the metallic glass parts has to be such that the time-temperature profile during cooling does not traverse through the nose-shaped region bounding the crystallized region in the TTT diagram. In FIG. 4, T_(noise) is the critical crystallization temperature where crystallization is most rapid and occurs in the shortest time scale.

The supercooled liquid region is between T_(g) and T_(x), which is a manifestation of the stability against crystallization of bulk solidification alloys. In this temperature region, the bulk solidifying alloy can exist as a high viscous liquid. The viscosity of the bulk solidifying alloy in the supercooled liquid region can vary between 10¹² Pa s at the glass transition temperature down to 10⁵ Pa s at the crystallization temperature, the high temperature limit of the supercooled liquid region. Liquids with such viscosities can undergo substantial plastic strain under an applied pressure. The embodiments herein make use of the large plastic formability in the supercooled liquid region as a forming and separating method.

The nose-shaped curve 408 shown in the TTT diagram is a function of temperature and time. To the right side of the nose-shaped curve 408, the alloy is in a crystalline phase. In FIG. 4, crystallization temperature T_(x) is shown as a dashed line, and may vary from near T_(m) to near T_(g). T_(x) may vary with alloy compositions.

The schematic TTT diagram of FIG. 4 shows processing methods of thermoplastic forming from at or above T_(g) to below T_(x) without the time-temperature trajectory (shown as 402 and 404 as an example trajectories) hitting the TTT crystallization curve 408. During thermoplastic forming, the forming takes place substantially simultaneously with fast cooling to avoid the trajectory hitting the TTT crystallization curve 408.

As shown by trajectory 402, the alloy may be heated to T_(processing) from a temperature below T_(g) and remains at T_(processing) for a first period of time and is then cooled or quenched to below T_(g), as pointed to by an arrow. With this trajectory 402, the alloy will not crystallize after thermoplastic forming.

As shown by trajectory 404, the alloy may be heated to T_(processing) from a temperature below T_(g) and remains at T_(processing) for a second period of time and is then cooled or quenched to below T_(g), as pointed to by an arrow. The second period of time is longer than the first period of time for trajectory 402. With this trajectory 404, the alloy will not crystallize after thermoplastic forming.

As shown by trajectory 404, the alloy may be heated to T_(processing) from a temperature below T_(g) and remains at T_(processing) for a third period of time which is long enough to cross or hit the TTT crystallization curve 408, and is then cooled or quenched to below T_(g), as pointed to by an arrow. The third period of time is longer than the second period of time for trajectory 404. With this trajectory 406, the alloy will crystallize after thermoplastic forming.

The processing methods for thermoplastic forming from at or above T_(g) to below T_(x) without the time-temperature trajectory (shown as 402 and 404 as example trajectories) hitting the TTT crystallization curve 408. If one heats up a piece of amorphous alloy but manages to avoid hitting the TTT crystallization curve 408, one heats the alloy “between T_(g) and T_(x)”, but one would have not reached T, However, the time-temperature trajectory 406 hits the TTT crystallization curve 408, which results in crystallization of the alloy.

Typical differential scanning calorimeter (DSC) heating curves of bulk-solidifying amorphous alloys taken at a heating rate of 20° C./min describe, for the most part, a particular trajectory across the TTT data where one would likely see a T_(g) at a certain temperature, a T_(x) when the DSC heating ramp crosses the TTT crystallization onset, and eventually melting peaks when the same trajectory crosses the temperature range for melting. If one heats a bulk-solidifying amorphous alloy at a rapid heating rate as shown by the ramp up portion of trajectories 402 and 404 in FIG. 4, then one could avoid the TTT crystallization curve 408 entirely, and the DSC data would show a glass transition but no T_(x) upon heating. Another way to think about it is trajectories 402 and 404 can fall anywhere in temperature between the nose of the TTT crystallization curve 408 (and even above it) and the T_(g) line, as long as it does not hit the TTT crystallization curve 408. That means that the horizontal plateau in trajectories might get much shorter as the processing temperature increases.

When the temperature T_(processing) in a supercooled liquid region (SLR) is higher, it provides a larger temperature window between the glass transition temperature T_(g) and the crystallization temperature T_(x) of a metallic glass former, but a less processing time t_(processing) for thermoplastic processing. As illustrated in FIG. 4, if a metallic glass former is treated by the temperature routine without crossing the TTT crystallization curve 408, such as trajectory 402 and 404, the metallic glass keeps the amorphous phase after the thermoplastic processing. However, when the trajectory 406 crosses the crystallization curve 408 into the crystalline region, the metallic glass will be crystallized.

For thermoplastic forming of metallic glasses, the challenge is avoiding crystallization. In one embodiment, the processing time t_(processing) is shortened as much as possible. However, the time window t_(processing) is generally quite limited for most metallic glass formers. The time window greatly limited the potential applications of thermoplastic forming of metallic glasses. During the thermoplastic forming of the metallic glasses, it is important to prevent crystallization or avoid oxidation in the thermoplastically forming metallic glasses.

Some metallic glasses may be more susceptible to oxidation than others. For example, Zr-based metallic glasses may be more susceptible to oxidation than Pt-based metallic glasses.

Additives may be included in the metallic glasses for suppressing crystallization and oxidation. For example, both oxidation reactions and crystallization of amorphous oxide films may be suppressed by the addition of beryllium to Zr—Cu alloys.

FIG. 5 is a flow chart illustrating thermoplastic forming a metallic glass with a fine texture replicating the surface texture of a glass mold in an embodiment of the disclosure. A metallic glass sheet is obtained to fit a required thickness and area for an intended use. For example, a metallic glass sheet having a thickness and area that corresponds to a cover for a handheld electronic device.

In operation 502, a metallic glass sheet is placed in a glass mold, for example, as shown in FIG. 3. The glass mold may have a fine textured surface formed by chemical etching, for example, as shown in FIGS. 2A-B. The method continues to operation 504.

In operation 504, the glass mold and the metallic glass sheet are heated to above the glass transition temperature of the metallic glass sheet, but below the crystallization temperature T_(x), such as trajectory 402 and/trajectory 404, which do not cross the TTT crystallization curve 408. The method continues to operation 506.

In operation 506, a pressure is applied through the glass mold, to conform the metallic glass sheet to a contoured shape of the mold to form a contoured sheet. The method continues to operation 508.

In operation 508, the mold is cooled such that an article is formed. The article replicates the texture of the glass mold.

Thermoplastic forming parameters, such as processing temperature, pressure, cooling rate, presence of vacuum, and the like, can be altered or modified to imprint the texture from the glass mold to the article.

In some variations, the thermoplastic forming method is a rapid discharge forming technique. In this process, the metallic glass is heated rapidly on a milliseconds time scale to a temperature that can be above T_(x) but below liquidus temperature. The metallic glass can be heated, formed, and cooled rapidly such that it does not intersect the nose of the TTT curve. Examples of rapid capacitor discharge forming can be found, for example, at U.S. Patent Publication No. 2014/0345350, incorporated by reference in its entirety.

After thermoplastic forming and creating a texture on the metallic glass, the metallic glass may be used in the “as-formed” condition or further treated to modify the surface. The additional modification can include mechanical, chemical, and electrochemical methods known in the art to further modify the surface structure.

Sa and Sq are two dimensional roughness based surface area measurements. Sa is the arithmetic average value of roughness, while Sq is the root mean squared value.

The variation Sa is the absolute value of the difference between Sa for glass mold and Sa for a metallic glass sample. The variation (Sa) % is the variation Sa divided by the Sa for the glass mold. Similarly, the variation Sq is the absolute value of the difference between Sq for glass mold and Sq for a metallic glass sample. The variation (Sq) % is the variation Sq divided by the Sq for the glass mold.

Note that these roughness parameters (Sq, Sa) may vary with the location for the same sample. The roughness measurements were not performed on a spot of the glass (e.g., silicate) mold and on the mirror of the spot on a finished part of the metallic glass samples.

In some embodiments, Sa can be within 20% of the glass mold. In some embodiments, Sa can be within 15% of the glass mold. In some embodiments, Sa can be within 10% of the glass mold. In some embodiments, Sa can be within 5% of the glass mold. In some embodiments, Sa can be within 3% of the glass mold. In some embodiments, Sa can be within 2% of the glass mold. In some embodiments, Sa can be within 1% of the glass mold.

In some embodiments, Sq can be within 20% of the glass mold. In some embodiments, Sq can be within 15% of the glass mold. In some embodiments, Sq can be within 10% of the glass mold. In some embodiments, Sq can be within 5% of the glass mold. In some embodiments, Sq can be within 3% of the glass mold. In some embodiments, Sq can be within 2% of the glass mold. In some embodiments, Sq can be within 1% of the glass mold.

Metallic Glasses

In many embodiments, the metallic glass has a base metal that is a late-transition metal. For example, the base metal of the metallic glass may be Pd, Pt, Au, Ni, Fe, Co, or Cu. In other embodiments, the metallic glass may contain at least one metalloid, semimetal, or nonmetal. For example, the metallic glass may contain one of P, Si, B, C, or combinations thereof. In yet other embodiments, the base metal of metallic glass may be a metal from the Iron Triad comprising Ni, Fe, Co, or combinations thereof, it may contain other transition metals such as Cr, Mo, Mn, Nb, Ta or combinations thereof at a combined atomic concentration ranging between 2 and 20%, and elements such P, B, Si, Ge, C or combinations thereof at a combined atomic concentration ranging between 15 and 25%.

The metallic glass can be any metallic glass known in the art. Without wishing to be held to a particular mechanism or mode of action, in some instances the method can be more effective with metallic glasses containing elements that are reactive with oxygen. For example, zirconium is more reactive with oxygen than platinum. A zirconium-based metallic glass can adhere more closely to a glass (e.g., silicate) mold than would a platinum-based metallic glass. When the Zr-based metallic glass (e.g. the LM105 metallic glass) is used, a normal oxidized color is blue on the surface.

The metallic glass can include any combination of the above elements in its chemical formula or chemical composition. The elements can be present at different weight or volume percentages. Alternatively, in one embodiment, the above-described percentages can be volume percentages, instead of weight percentages. Accordingly, a metallic glass can be zirconium-based (Zr-based), platinum-based (Pt-based), iron-based (Fe-based), nickel-based (Ni-based), titanium-based (Ti-based), palladium-based (Pd-based), gold-based (Au-based), silver-based (Ag-based), copper-based (Cu-based), aluminum-based (Al-based), molybdenum-based (Mo-based), magnesium-based (Mg-based), and the like. The metallic glass can also be free of any of the aforementioned elements to suit a particular purpose. For example, in some embodiments, the metallic glass can be substantially free of nickel, aluminum, titanium, beryllium, or combinations thereof. In one embodiment, the metallic glass or the composite is completely free of nickel, aluminum, titanium, beryllium, or combinations thereof.

Furthermore, the metallic glass can also be one of the exemplary compositions described in U.S. Patent Application Publication Nos. 2010/0300148 or 2013/0309121, the contents of which are herein incorporated by reference.

The metallic glass can also be a ferrous metallic glass, such as (Fe, Ni, Co) based metallic glasses. Examples of such compositions are disclosed in U.S. Pat. Nos. 6,325,868; 5,288,344; 5,368,659; 5,618,359; and U.S. Pat. No. 5,735,975, Inoue et al., Appl. Phys. Lett., Volume 71, p 464 (1997), Shen et al., Mater. Trans., JIM, Volume 42, p 2136 (2001), and Japanese Patent Application No. 200126277 (Pub. No. 2001303218 A). One exemplary composition is Fe₇₂Al₅Ga₂P₁₁C₆B₄. Another example is Fe₇₂Al₇Zr₁₀Mo₅W₂B₁₅. Another iron-based metallic glass system that can be used in the coating herein is disclosed in U.S. Patent Application Publication No. 2010/0084052, wherein the amorphous metal contains, for example, manganese (1 to 3 atomic %), yttrium (0.1 to 10 atomic %), and silicon (0.3 to 3.1 atomic %) in the range of composition given in parentheses; and that contains the following elements in the specified range of composition given in parentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic %), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to 16 atomic %), and the balance iron.

The aforementioned metallic glass systems can further include additional elements, such as additional transition metal elements, including Nb, Cr, V, and Co. The additional elements can be present at less than or equal to about 30 wt %, such as less than or equal to about 20 wt %, such as less than or equal to about 10 wt %, such as less than or equal to about 5 wt %. In one embodiment, the additional, optional element is at least one of cobalt, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium, and hafnium to form carbides and further improve wear and corrosion resistance. Further optional elements may include phosphorous, germanium, and arsenic, totaling up to about 2%, and preferably less than 1%, to reduce melting point. Otherwise incidental impurities should be less than about 2% and preferably 0.5%.

In some embodiments, a composition having a metallic glass can include a small amount of impurities. The impurity elements can be intentionally added to modify the properties of the composition, such as improving the mechanical properties (e.g., hardness, strength, fracture mechanism, etc.) and/or improving the corrosion resistance. Alternatively, the impurities can be present as inevitable, incidental impurities, such as those obtained as a byproduct of processing and manufacturing. The impurities can be less than or equal to about 10 wt %, such as about 5 wt %, such as about 2 wt %, such as about 1 wt %, such as about 0.5 wt %, and such as about 0.1 wt %. In some embodiments, these percentages can be volume percentages instead of weight percentages. In one embodiment, the metallic glass sample/composition consists essentially of the metallic glass (with only a small incidental amount of impurities). In another embodiment, the composition includes a metallic glass (with no observable trace of impurities).

In other embodiments, metallic glasses, for example, of boron, silicon, phosphorus, and other glass-formers with magnetic metals (iron, cobalt, nickel) may be magnetic, with low coercivity and high electrical resistance. The high resistance leads to low losses by eddy currents when subjected to alternating magnetic fields, a property useful, for example, as transformer magnetic cores.

In further embodiments, the alloy can be a composite of a crystalline alloy and a metallic glass. Examples of such composites can be made from Zr, Au and other alloys that contain amorphous and crystalline character. Any metallic glass—alloy composite known in the art can be used.

The disclosed metallic glasses and methods can be used in the fabrication of electronic devices. An electronic device herein can refer to any electronic device known in the art. For example, such devices can include wearable devices such as a watch (e.g., an AppleWatch®). Devices can also be a telephone such a mobile phone (e.g., an iPhone®) a land-line phone, or any communication device (e.g., an electronic email sending/receiving device). The metallic glasses can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad®), and a computer monitor. Metallic glasses can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod®), etc. Metallic glasses can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV®), or can be a remote control for an electronic device. Metallic glasses can be a part of a computer or its accessories, such as the hard drive tower housing or casing.

EXAMPLE

The following example is intended to illustrate aspects of the disclosure, and should not be interpreted as limiting any aspect of the disclosure in any capacity.

Several metallic glasses were molded by the method disclosed above and demonstrate that the fine texture was replicated from the glass mold. For example, Zr-based metallic glasses, e.g. Zr₇₀Cu₁₃Ni_(9.9)Al_(3.7)Nb_(3.4), Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8), and Zr₄₁Ti₁₄Cu₁₂Ni₁₀Be₂₃, were tested for trials. Pt-based metallic glass, such as Pt_(57.3)Cu_(14.7)Ni_(5.3)P_(22.7), was also tested for trials.

Table 1 lists the physical and mechanical properties of samples. Table 1 provides the compositions for metallic glass Samples 1-4. For example, Sample 1 included 70 wt % Zr, 13 wt % Cu, 9.9 wt % Ni, 3.7 wt % Al, and 3.4 wt % Nb. Sample 2 included 67 wt % Zr, 8.8 wt % Ti, 9.8 wt % Ni, 10.6 wt % Cu, and 3.3 wt % Be. Sample 3 included 57.3 wt % Pt, 14.7 wt % Cu, 5.3 wt % Ni, and 22.7 wt % P. Sample 4 included 41 wt % Zr, 14 wt % Ti, 12 wt % Cu, 10 wt % Ni, and 23 wt % Be.

Table 1 also provides the glass transition temperature T_(g), crystallization temperature T, and melting point T_(m) for each sample. Table 1 also provides the physical properties including density, fracture toughness, and tensile strength for Samples 1-4. As shown in Table 1, the metallic glasses may vary in density, fracture toughness and tensile yield strength.

TABLE 1 Physical and Mechanical Properties of Metallic Glass Samples Tensile Fracture yield T_(g) T_(x) T_(m) Density Toughness strength Sample Amorphous alloy (° C.) (° C.) (° C.) (g/cc) (MPa-m^(1/2)) (MPa) 1 Zr₇₀Cu₁₃Ni_(9.9)Al_(3.7)Nb_(3.4) 395 499 837 6.7 30 1800 2 Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8) 352 466 644 6.0 55 1800 4 Zr₄₁Ti₁₄Cu₁₂Ni₁₀Be₂₃ 355 429

In these trials, each of the metallic glass samples 1-4 was heated up to a processing temperature T_(processing) above the glass transition temperature T_(g) and a pressure was applied to a glass mold using the thermoplastic forming disclosed above.

Table 2 lists the processing temperature T_(processing), applied pressure, and time T_(processing) for replicating the surface texture of a glass mold.

TABLE 2 Processing Conditions of Metallic Glass Samples Applied Sam- T_(processing) Pressure t_(processing) ple Amorphous alloy (° C.) (KN) (min.) 1 Zr₇₀Cu₁₃Ni_(9.9)Al_(3.7)Nb_(3.4) 470 5 3.5 2 Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8) 430 6 3.0 3 Pt_(57.3)Cu_(14.7)Ni_(5.3)P_(22.7) 270 2 3.0

As listed in Table 2, the processing temperature is 470° C. for Sample 1. This processing temperature was above the T_(g) of Sample 1, i.e. 395° C., but was below the crystallization temperature T_(x), i.e. 499° C., as listed in Table 1. The applied pressure is 5 KN, and the processing time is 3.5 minutes for Sample 1.

Also, the processing temperature is 430° C. for Sample 2. This processing temperature was above the T_(g) of Sample 2, i.e. 352° C., but was below the crystallization temperature T, i.e. 466° C., as listed in Table 1. The applied pressure is 6 KN, and the processing time is 3.0 minutes for Sample 2.

Referring to Sample 3 now, the processing temperature was 270° C. for Sample 3. This processing temperature was above the T_(g) of Sample 3, but was below the crystallization temperature T_(x), as listed in Table 1. The applied pressure is 2 KN, and the processing time is 3.0 minutes for Sample 3.

FIG. 6 illustrates an image of a glass mold texture in accordance with an illustrative embodiment. As shown, a number of small circular dimples 602 appear on the surface and are typically about 1-3 μm in depth, with some larger dimples 604 having depth of at least 6 μm.

Some sub-micron texture features also appear to be replicated. Several example amorphous alloys (Samples 1-3) all demonstrate viable for thermoplastic forming of a glass mold. The experiments successfully replicated the negative of the glass mold with features (e.g., bumps) that are typically about 1-3 μm and some other features (bumps) are at least 6 μm in depth.

FIG. 7 illustrates a replicate texture of the glass mold of FIG. 6 for amorphous alloy Zr₇₀Cu₁₃Ni_(9.9)Al_(3.7)Nb_(3.4) in accordance with an illustrative embodiment. As shown, a number of small circular dimples 702 appear on the surface and are typically about 1-3 μm in depth, with some larger dimples 704 having depth of at least 6 μm.

FIG. 8 illustrates a replicate texture of the glass mold of FIG. 6 for amorphous alloy Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8) in accordance with an illustrative embodiment.

FIG. 9 illustrates a replicate texture of the glass mold of FIG. 6 for amorphous alloy Pt_(57.3)Cu_(14.7)Ni_(5.3)P_(22.7) in accordance with an illustrative embodiment.

As shown, the surface textures for the various amorphous alloys, as illustrated in FIGS. 7, 8, and 9, are similar to that shown in FIG. 6 for glass mold.

Sample 4 reveals similar results to Samples 1-3.

Table 3 depicts the surface roughness data obtained for Samples 1-4 listed in Table 1.

TABLE 3 Comparison of Surface Roughness of Silicate Mold versus Metallic Glass Samples Sa Sq Variation Variation Sample Composition (μm) (μm) (Sa) % (Sq) % Silicate Mold 0.8175 1.063 0 0 1 Zr₇₀Cu₁₃Ni_(9.9)Al_(3.7)Nb_(3.4) 0.7225 0.8963 11.6 16.2 2 Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8) 0.8023 1.100 1.9 3.5 3 Pt_(57.3)Cu_(14.7)Ni_(5.3)P_(22.7) 0.8953 1.261 9.5 18.6

As shown, metallic glass Zr₆₇Ti_(8.8)Ni_(9.8)Cu_(10.6)Be_(3.8) has the smallest variation from the silicate glass, while all metallic glass samples 1-3 have variations in Sa and Sq from the silicate mold less than 20%.

Any metallic glass or amorphous alloy in the art may be used in connection with the methods and apparatuses described herein.

Any ranges cited herein are inclusive. The terms “substantially” and “about” used throughout this Specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.

Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the invention. Accordingly, the above description should not be taken as limiting the scope of the invention. Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the method and system, which, as a matter of language, might be said to fall therebetween. 

What is claimed is:
 1. A method of thermoplastic forming a metallic glass comprising: placing a metallic glass on a glass mold having a portion of a surface with a fine surface texture; heating the glass mold to a processing temperature above the glass transition temperature of the metallic glass; applying a pressure to the glass mold; and cooling the metallic glass to form an article replicating the fine surface texture from the portion of the glass mold.
 2. The method of claim 1, wherein the fine surface texture has a surface depth in the micron range.
 3. The method of claim 1, wherein the portion of the surface of the glass mold is chemically etched.
 4. The method of claim 1, wherein the metallic glass comprises a material selected from a group consisting of Zr-based, Pt-based, Ni-Based, Fe-based, Ti-based, Pd-based, Au-based, Ag-based, Cu-based, Al-based, and Mo-based.
 5. The method of claim 1, wherein the processing temperature is lower than the crystallization temperature of a metallic glass.
 6. The method of claim 1, wherein the article is in an amorphous phase.
 7. The method of claim 1, wherein the metallic glass has a TTT crystallization curve.
 8. The method of claim 7, wherein a trajectory of the processing temperature versus time does not cross the TTT crystallization curve to void crystallization.
 9. The method of claim 1, wherein the metallic glass comprises a metallic glass feedstock in a form of sheet, film, or rod.
 10. The method of claim 1, wherein the glass mold is a silicate glass mold.
 11. The method of claim 1, wherein the glass surface texture is a silicate glass surface texture.
 12. A metallic glass having a fine surface texture as a glass surface texture, wherein the fine surface texture has a surface roughness ranging from 0.1 μm to 10 μm or a surface depth variation from −3 μm to 10 μm.
 13. The metallic glass of claim 12, wherein the surface depth is from −1 μm to 3 μm.
 14. The metallic glass of claim 12, wherein the surface roughness is from 0.1 μm to 3 μm.
 15. The metallic glass of claim 12, wherein the metallic glass comprises a material selected from a group consisting of Zr-based, Pt-based, Ni-Based, Fe-based, Ti-based, Pd-based, Au-based, Ag-based, Cu-based, Al-based, and Mo-based.
 16. The metallic glass of claim 12, wherein the fine surface texture has a surface roughness Sa within 30% of the Sa of the glass mold.
 17. The metallic glass of claim 12, wherein the fine surface texture has a surface roughness Sq within 30% of the Sq of the glass mold.
 18. The metallic glass of claim 12, wherein the glass surface texture is a silicate glass surface texture.
 19. The metallic glass of claim 12, wherein the glass surface texture is obtained by chemical etching.
 20. The metallic glass of claim 12, wherein the fine surface texture is formed from thermoplastic forming. 